Cell-based therapies provide a novel approach to treating chronic diseases. Recapitulating a damaged organ's function by secreting hormones or other factors is dependent upon successful engraftment of transplanted cells. Engraftment of the transplanted cells requires that cells survive the initial hypoxic environment following transplantation, connect with the host vasculature for exchange of nutrients and waste products and also deliver secreted factors into the circulation. Doing this requires creating an environment that promotes long term function of the transplanted cells. If the cell supply is limited, approaches to expand the transplant graft in vivo may also be important. We propose to address the hypothesis that micro-porous polymer scaffolds capable of delivering biologically active peptides can create a microenvironment to promote cell engraftment, survival and proliferation. A classic paradigm for cell-based therapy is islet transplantation for treatment of type 1 diabetes in which destruction of insulin-secreting beta cells in the pancreas results in hyperglycemia and its complications. Recent trials have provided proof of concept that islet transplantation can be efficacious, yet problems remain. To address these problems, we are proposing to transplant islets on microporous scaffolds capable of releasing proteins that can influence the host tissue (e.g., vascularization) or enhance the functionality of the transplanted islets. These factors will condition the microenvironment to promote islet engraftment, survival, and function. We have recently shown that microporous scaffolds can serve as a platform for islet transplantation. The Specific Aims are as follows. (i) 1) To investigate the hypothesis that the scaffold architecture, as defined by porosity, pore size, and stability, will influence islet engraftment and function. (ii) To address the hypothesis that use of a polymer scaffold to deliver angiogenic factors will improve islet survival and function post-transplantation in a murine model of diabetes. (iii) To test the hypothesis that polymer scaffolds delivering factors that inhibit islet cell death and/or increase islet cell mass post-transplantation will enhance islet engraftment and function. (iv) To determine whether delivering a combination of growth factors that affect different processes (e.g., angiogenesis and islet cell survival and/or proliferation) is more efficacious than delivering a single factor. These studies have the potential to substantially advance cell therapies for islet transplantation.